1. Field of the Invention
The present invention relates to a compound semiconductor image sensor including photoelectric conversion units which are vertically stacked and which absorb light of different wavelengths.
2. Description of the Related Art
An image sensor using a photoelectric transducer which detects light and converts the light into an electrical signal includes plurality of unit pixels arranged in matrix on a semiconductor substrate. Each of the unit pixels includes a photodiode and transistors.
A conventional complimentary metal oxide semiconductor (“CMOS”) image sensor includes a CMOS control element and a photodiode which receives and stores optical signals. The conventional CMOS image sensor may be manufactured on a single chip along with signal processing elements.
In the conventional CMOS image sensor, the photodiode includes a color filter which transmits light of a particular wavelength. Since the color filter absorbs approximately ⅔ of light incident on the photodiode, the amount of light input to the photodiode is reduced, which causes a reduction in the sensitivity of the conventional CMOS image sensor.
U.S. Patent Publication No. 2005/0194653, discloses an CMOS image sensor, which does not use a color filter. In this CMOS image sensor, vertically stacked photodiodes generate electrical signals.
Also, U.S. Patent Publication No. 2005/0205903 discloses a CMOS image sensor, which does not use a color filter. In this CMOS image sensor, a photoelectric conversion film is used as a photoelectric conversion unit.